As conventional materials of fitting type connecting terminals wherein one of male and female terminals is fitted into the other terminal, there are used tin-plated products wherein a tin plating layer is formed as the outermost layer on a conductive material, such as copper or a copper alloy. In particular, tin-plated products have a small contact resistance, and are used as the materials of various connecting terminals for automotive vehicles, information and communication apparatuses, industrial apparatuses and so forth, from the standpoint of contact reliability, corrosion resistance, solderability, economical efficiency and so forth.
In recent years, connecting terminals for automotive vehicles and so forth are miniaturized, so that the thickness of spring portions thereof is decreased. In addition, it is not possible to sufficiently ensure spring displacement, so that the contact load at the contact point between male and female terminals is decreased. Particularly in fitting type connecting terminals of tin-plated products, if the contact load at the contact point between male and female terminals is decreased, there is a problem in that the contact reliability thereof is deteriorated by minute sliding abrasion due to minute sliding at the contact point.
In order to eliminate this problem, it is proposed to form an Ag—Sn alloy layer on the surface of a tin plating layer, which is formed on a base material of a small terminal, to suppress the rise of electric contact resistance due to the minute sliding abrasion of the small terminal to enhance the electric connection reliability thereof (see, e.g., Japanese Patent Laid-Open No. 2010-37629).
It is also proposed to provide a reinforcing member having a spring piece for reinforcing the contact pressure of a contact piece to obtain a strong contact pressure at which it is difficult to cause minute sliding abrasion due to vibration (see, e.g., Japanese Patent laid-Open No. 2006-134681), and to provide a holding portion for holding the tip portion of a tab of a mating terminal in a relative displacement regulated state to prevent the minute sliding abrasion between terminal fittings (see, e.g., Japanese Patent Laid-Open No. 2006-80004).
Moreover, it is proposed to provide prismatic protruding portions on an electric contact of one connector of an electric connector assembly to cause the electric contact of the other connector to slide thereon, so that it is difficult to allow impurities, such as solder, to adhere to the electric contact of the electric connector while it is difficult to cause contact failure (see, e.g., Japanese Patent Laid-Open No. 2001-266990). It is also proposed to cause the sliding distance producible between the male and female terminals in a state that a male connector is fitted into and fixed to a female connector to be less than the range of contact flaws in a contact range in which the contact portion of the male terminal contacts that of the female terminal, so that contact reliability is prevented from being deteriorated even under a high sliding environment (see, e.g., Japanese Patent Laid-Open No. 2005-141993).
However, as described in Japanese Patent Laid-Open No. 2010-37629 in which the Ag—Sn alloy layer is formed on the surface of the tin plating layer, if a conductive material is plated with an expensive noble metal, such as Au or Ag, as the outermost thereof or if a high strength material is used as a conductive material to increase contact load, the costs thereof are very high.
Also, even if the movement of the contact portion is prevented by the structure of the terminal so as to prevent sliding as described in Japanese Patent Laid-Open Nos. 2006-134682 and 2006-80004, if the contact load decreases in a fitting type connecting terminal of a tin-plated product, the contact point is easy to move, so that it is difficult to suppress the minute sliding abrasion due to minute sliding.
Moreover, if the prismatic protruding portions are provided on the electric contact of one connector of the electric connector assembly as described in Japanese Patent Laid-Open No. 2001-266990, or if the sliding distance producible between the male and female terminals while a male connector is fitted into and fixed to a female connector is caused to be less than the range of contact flaws in a contact range in which the contact portion of the male terminal contacts that of the female terminal as described in Japanese Patent Laid-Open No. 2005-141993, it is not possible to sufficiently prevent oxides of abrasion powder of Sn plating produced during minute sliding from being accumulated on the contact portion to restrain the minute sliding abrasion in a fitting type connecting terminal of a tin-plated product.